Stretched texture with Principled texture setup
The shader uses UV map of the object if it is available.
If you modifiy the object mesh after the UV map has been defined (and base objects have a default UV map), then Blender can't guess where to place the UV part of new geometry or how to move the already existing one of changed parts of the mesh.

And as result,the UV map part of these new faces are flat:

So to solve it, depending on your case, you can either make the UV map again, or change the texture coordinates in the shader.
Here for instance, &quot;generated&quot; texture coordinates and the image texture changed to &quot;box&quot;:

The documentation of the texture coordinates node here.
And some practical information about it from Blender Guru here.
In case it is useful, a UV map is a map that defines the correspondence between 3D faces of the model and 2D parts of these faces on a texture.